# FFT and IFFT

Started by March 22, 2001
 Hi Everyone,       I have a matlab problem which has been bothering me.       I have a vector A of 512 music samples consisting of positive and negative values betw -1 and 1.     Eg A = 1.0e-004 * [  -0.0946   -0.1547   -0.0371   -0.2034    0.0861   -0.0713    0.0288 0.1651   -0.1140    0.1537 ...........]       I have another vector B, which is a result of A, after undergoing only some minor modifications.     Eg  B = 1.0e-004 *[  -0.0945   -0.1547   -0.0371   -0.2035    0.0861   -0.0713    0.0289 0.1651   -0.1140    0.1537 ...........]       I found a very strange thing:       Only the 1st to 233th values and 281th to 512th values of fft(A) and fft(B) are almost exactly the same.     The 234th to 280th values differ by a magnitude of almost 100 to 700!!         My thinking: I thought all the components in fft(A) should rightfully be ALMOST equal to fft(B) since B is almost the same as as A??   Can anyone enlighten me please?? Will appreciate any help. Tks!   Tks!   Rgds Kelvin